ObjC test failures, sparc-sun-solaris2.6

[Zack Weinberg]

All the ObjC tests fail to link on sparc-sun-solaris2.6 right now.
This is because libobjc wants to use sched_yield which is in libposix4
which is not referenced:

/attic/source/sandbox/build/gcc/xgcc 
	-B/attic/source/sandbox/build/gcc/
	/attic/source/sandbox/egcs/gcc/testsuite/objc/execute/bf-1.m -w -O
	-I/attic/source/sandbox/egcs/gcc/testsuite/../../libobjc
	-L/attic/source/sandbox/build/sparc-sun-solaris2.6/libobjc -lobjc -lm
	-o /attic/source/sandbox/build/gcc/testsuite/bf-1.x
Undefined                       first referenced
 symbol                             in file
sched_yield                         libobjc.a(thr-posix.o)
ld: fatal: Symbol referencing errors. No output written to bf-1.x
collect2: ld returned 1 exit status
compiler exited with status 1

We need some way of getting an -lposix4 in there when necessary.  I'll
leave this to the ObjC and testsuite experts.

zw